Femoral bone strains during antegrade nailing: a comparison of two entry points with identical nails using finite element analysis.

BACKGROUND

Antegrade femoral nailing has become the standard treatment for diaphyseal femoral shaft fractures. Concerns linger that improper location of the nail entry point may lead to iatrogenic fracture and further complications. This study used finite element analysis to compare the strain magnitude and distribution resulting from each of two entry points in the proximal femur during antegrade nailing.

METHODS

A finite element model was created from a CT scan of a 37 year old male femur and of a standard antegrade nail. Using implicit time-stepping, the nail was inserted through piriformis and trochanteric entry points and strain was computed at 9 anatomic locations.

FINDINGS

The strain levels were higher overall when inserting a nail through the trochanteric starting point. The highest strain occurred immediately medial and lateral to the trochanteric entry point. The posterior greater trochanter also showed very high strain levels during nail insertion. All strain values for nail insertion through the piriformis entry point were less than 2000 μm/m.

INTERPRETATION

The trochanteric entry will have a much greater potential of iatrogenic fracture of the proximal femur during insertion of a nail. Strains with this entry point exceed the yield level of bone and the repeated loading with the progression of the nail could cause fissures or fractures. Caution should be taken during insertion of an antegrade nail when utilizing a lateral trochanteric starting point secondary to an increased risk of trochanteric fracture and lateral cortex fracture.